This proposal requests funds for investigating the role of histamine in ovarian function of rats. The literature reveals that ovarian blood flow varies during the estrous cycle and that exogenous luteinizing hormone (LH) or histamine increases ovarian blood flow in immature and diestrus rats. In addition, LH causes histamine depletion from the ovary, and antihistamines block the LH-induced increase in ovarian blood flow. Antihistamine administration also blocks ovarian follicular growth in some species. The following hypotheses will be tested in this project: 1) The number and distribution of ovarian mast cells, histamine content of mast cells and ovarian tissue, and ability of LH to cause ovarian histamine depletion, vary with stage of the estrous cycle, 2) LH-induced histamine depletion is mediated by stimulation of estrogen secretion, 3) Removal of histamine from ovarian mast cells eliminates LH-induced histamine depletion, and 4) antihistamine blocks maturation of ovarian follicles and ovulation if administered at a given stage in the estrous cycle. Possible use of antihistamines for fertility control is a major concern of this project.